1. Field of the Invention
The invention is of a system for implanting soft tissue anchors for holding soft tissue in place relative to bone. More particularly, the invention provides a system for readily implanting soft tissue anchors as well as soft tissue anchors that are equipped with structural features preventing their inadvertent withdrawal from bone holes.
2. Description of the Related Art
In the field of surgery it is sometimes necessary to perform operations to reattach soft tissue to bone. For example, U.S. Pat. No. 4,924,865 describes a repair tack designed for use in arthroscopic surgery to repair a torn meniscus in the knee. Reattachment of soft tissue to bone may also arise, for instance, when surgery is performed on a shoulder to remove or repair glenohumeral tissue.
Regardless of the circumstance, whenever bone must be reattached to tissue, it is desirable to have a fastener or "anchor" that will hold the tissue onto the bone at its point of reattachment, and that will allow the tissue to heal and naturally reattach itself to the bone. Thus, it is desirable that the soft tissue fixation element should not interfere with the healing process and should allow progressively heavier loads to be placed on both bone and soft tissue to encourage healing and development of attachment strength.
U.S. Pat. Nos. 4,590,928 and 4,851,005 disclose surgical implants that include an expandable stud and a pin for insertion into the stud to expand the stud. The stud and pin are both fabricated from biodegradable polymeric materials, and include carbon fibers aligned along their longitudinal axes. The stud body has an enlarged head at one end and, at the opposite end, its cylindrical surface is longitudinally split. Further, the stud has a cylindrical bore running throughout its length along its longitudinal axis. The pin is inserted into this bore thereby forcing the split distal ends radially outwards, to expand the stud body and lodge it firmly in a hole in bone. The stud and pin combination is used to connect a synthetic flexible cord for holding two bones together in a mammalian body.
Likewise, U.S. Pat. 4,834,752 is directed to a "tissue augmentation device" for repairing ligaments or tendons. The device includes at least one strap-like element (substitute tendon) formed of stable biocompatible material and a biodegradable element for connecting the strap-like element to bone. The biodegradable fasteners shown in FIGS. 2 and 4 of the '752 patent, include a pin having a longitudinal body with a head at one end, a longitudinal bore through the body, and slits at the distal end of the body producing longitudinal distal segments. A pin is insertible into the bore of the body for expanding the segments radially outward so that they will grip the sides of a hole in bone. The embodiment of FIG. 4 shows barbs extending downward from the undersurface of the head for engaging the strap-like element and holding it in place.
EPO Application No. 0 409 364 shows a conical-shaped implant for joining together bone fragments. The longitudinal body of the implant is supplied with a conical axial hole, and a pin for inserting into the hole to expand the body of the implant, and wedge it firmly in surrounding bone tissue. The implant is bioresorbable to eliminate the need for later surgical removal. The outer surface of the implant is equipped with barb-like projections, presumably for assisting in holding the implant in place in the bone hole.
U.S. Pat. Nos. 4,590,928 and 4,851,005, likewise show an expandable stud for attaching a flexible cord, of biocompatible fibers in a biocompatible matrix, to bone. The stud has a longitudinal body with a head a one end, a bore extending along its longitudinal axis, and is split at its distal end to form separate legs so that when a pin is placed within the bore, it expands the legs radially outward to wedge the stud firmly in a hole.
What is yet needed is a surgical implantation kit that allows easy, accurate implantation of soft tissue anchors at desired bone-soft tissue contact points. The implanted anchors should grip soft tissue against the bone to promote rapid attachment and should decrease its gripping strength over time to gradually reduce stress shielding there by shifting stress loads to the soft tissue-bone interface so that the interface strengthens as it heals. Further, the anchors should be relatively small, to avoid drilling large holes in bone and soft tissue that increase healing time, but at the same time should resist being pulled out of the bone hole by applied forces.